Roll-to-roll method and system for micro-replication of a pattern of large relief three-dimensional microstructures

ABSTRACT

A method and system referred to as PALM (Patterning by Adhesive of Large Relief Three-Dimensional Microstructures) with large reliefs exceeding 1 μm and being as large as 100 μm. The microstructures can be either deterministic (such as microprisms), or random (such as diffusers), the first obtained by copying an original supermaster, and latter obtained by copying a laser speckle pattern. The master process entails copying a supermaster into the form of the microstructure constituting a pattern on the patterning cylinder (called a drum), to be then continuously multiplied in the PALM system, in a continuous roll-to-roll web process. The latter method, together with the related system, is the subject of this invention. The rolls continuously repeat the master pattern, copying by adhesive with large viscosity on acrylic (hybrid) as well as by a monolithic process. The monolithic process can be accomplished using temperature and pressure, or by UV-cured polymerization. Therefore, the invention comprises three alternative processes: one, hybrid (adhesive on acrylic), and two monolithic ones. In the PALM (hybrid) process, an epoxy is wet-coated on film substrates such as polycarbonate (PC), polyester (PET), (PE), or other flexible material. The adhesive, in liquid form, is applied to the substrate by a self-metered coating sub-process. In the present invention, the adhesive is used for forming the microstructure pattern. The microstructure pattern is replicated from a master roll or image drum onto a coating roll.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to the field of manufacturing byreplication of a master pattern. More specifically, the inventionrelates to roll-to-roll replication of high aspect ratiothree-dimensional microstructures from an image drum cylinder onto acontinuous band of curable liquid adhesive in a process herein calledPALM.

2. Background Art

In the present invention a liquid adhesive is applied, using aroll-to-roll technique to a drum having a microstructure pattern that isto be replicated onto a rolling flexible sheet or substrate. There arenumerous prior art patents which disclose this type of replicationprocess. By way of example, the assignee hereof has obtained U.S. Pat.Nos. 5,735,988 and 5,922,238 for replicating optical diffusers withshallow relief patterns. Others have disclosed similar replicationprocesses for creating microcup patterns for manufacturing LCD displays.See for example U.S. Pat. Nos. 6,933,098; 6,930,818; and 6,672,921.There are also numerous issued U.S. Patents relating to roll-to-rollreplication processes for fabricating retro-reflective sheeting and thelike such as U.S. Pat. Nos. 5,763,049 and 5,691,846. However, such priorart relates generally to either relatively low profile, small reliefpatterns with structures having peak heights of less than about 5μmeters or to higher relief structures having very regular and thushighly predictable relief patterns.

However, there is a need for employing such low cost, high yieldreplication processes for fabricating deep relief, large profile,irregular optical surfaces such as large angle diffusers with nospecular components and only diffuse components. It would be highlyadvantageous to provide a roll-to-roll microreplication system capableof fabricating accurate replications of patterns having reliefstructures from as small as 3μ meters to as large as 100μ meters.

SUMMARY OF THE INVENTION

The present invention comprises a method, system and device referred toas PALM (Patterning by Adhesive of Large Relief Three-DimensionalMicrostructures) with large reliefs exceeding 1 μm and being as large as100 μm. The PALM process is a web micropatterning process thatreplicates deep relief microstructures, both random and deterministic.These three-dimensional microstructures have resolving elements, d, downto the submicron range, but large RMS, up to 30 μm, or higher, withaspect ratios approaching, or exceeding unity (AR˜1). They can be foundin two-dimensional arrays (microprisms) and three-dimensional arrays(microlenses). The microstructures can be either deterministic (such asmicroprisms), or random (such as diffusers), the first obtained bycopying the original supermaster, and latter obtained by copying a laserspeckle pattern. The processes of creating the master are not thesubject of this invention. The master process entails copying asupermaster into the form of the microstructure constituting a patternon the patterning cylinder (called a drum), to be then continuouslymultiplied in the PALM system, in a continuous roll-to-roll web process.The latter method, together with the related system, is the subject ofthis invention. By “large area microstructures,” we mean themicrostructure produced on rolls, one foot, two feet or more (60 cm ormore) wide, and 1000 ft., 2000 ft. or more long. The rolls continuouslyrepeat the master pattern, copying by adhesive epoxy with largeviscosity on acrylic (hybrid) as well as by a monolithic process. Themonolithic process can be accomplished using temperature and pressure,or by UV-cured polymerization. Therefore, we consider three kinds ofprocesses: one, hybrid (adhesive on acrylic), and two monolithic ones.Typical structures are 36 in. (or 91 cm) wide.

In the PALM (hybrid) process, an adhesive is wet-coated on filmsubstrates such as polycarbonate (PC), polyester (PET), (PE), or otherflexible material, obtained from manufacturers such as DuPont, GE, orothers. The adhesive, in liquid form, is applied to the substrate by aself-metered coating sub-process, analogous to lubrication. This is atype of electrohydrodynamic lubrication, which is a phenomenon thatoccurs when a lubricant (here adhesive) is introduced between surfaceswhich are in rolling contact. In mechanical design literature(Mechanical Engineering Design by Shipley et al, 4^(th) Ed., Section12-4), such lubrication is introduced for motoring force transfer in amating press, or rolling bearing, or other, to avoid boundarylubrication. In the present invention, the adhesive (a lubricant) isused for forming the microstructure pattern. The microstructure patternis transferred (replicated) from a master roll (a drum) onto a coatingroll. The general architecture of the PALM process is shown in FIG. 1.The unwind roll containing substrate is transformed, through the PALMprocess, into a re-wind roll containing a substrate with coatedadhesive, including a replicated microstructure pattern. Typically,optical adhesive, which must be transparent to light, (especially, insolid form) and have desired optical properties, such as a refractiveindex, which should typically have a value close to that of thesubstrate, is used for providing optical contact (without air gap)between two optical layers. Here, in addition to the above property, itshould have the ability to follow the analog master micropattern, aswell as other properties such as high viscosity and proper surfaceenergy, discussed below. By “analog” structure, we mean that in theideal case, the three-dimensional master relief pattern should beprecisely replicated into the three-dimensional copy. This is achallenge, especially for relief microstructures approaching 100 μm (or4 mil), not only with micro or sub-micro resolution details, d, and withaspect ratio, (AR), approaching, or exceeding 1-3 range up to 50 μm, oreven higher, where, here the aspect ratio is defined as ratio of rootmean square (RMS), δ, into resolution detail, d, as shown in FIG. 2, fora random microstructure:

$\begin{matrix}{{({AR})^{\Delta} = \frac{\delta}{d}}\text{where}} & (1) \\{\delta = {{RMS} = \sqrt{\langle\left( {z - z_{0}} \right)^{2}\rangle}}} & (2)\end{matrix}$

where < . . . > is ensemble average, as defined in statistical opticsliterature, and the coordinate z₀, is defined in such a way that

(z−z ₀)=0   (3)

The two-dimensional version of random pattern is shown in FIG. 2. Thisfigure is only for simplification since the real random pattern isthree-dimensional, as in FIG. 5. In typical scattering modelingtheories, the resolving element, d, is replaced by correlation length ξ,discussed in X-ray scattering for rough surfaces. By applying so-calledergodic hypothesis, the ensemble average can be replaced by integrationover single statistical realization, in the form:

$\begin{matrix}{{\langle\left( {z - z_{0}} \right)^{2}\rangle} = {\lim\limits_{{\Delta \; x}->\infty}{\frac{1}{\Delta \; x}{\int_{{- \Delta}\; {x/2}}^{\Delta \; {x/2}}{\left( {z - z_{0}} \right)^{2}{x}}}}}} & (4)\end{matrix}$

where z(x) is a function shown in FIG. 2. These definitions can be alsoapplied for the deterministic (regular) patterns such as microprismarray, as in FIG. 3, or other regular repeatable relief patterns, withtwo-dimensional arrays (microprisms), or three-dimensional arrays(microlenses).

The microprisms patterns can be used as Directional Turning Films(DTFs), Brightness Enhancing Films (BEFs), and the like. The randomstructures can be Lambertian or non-Lambertian diffusers. In general, inthe case of analog microstructures as discussed above, we should avoidsharp edges, marked by circles in FIGS. 2 and 3. Nevertheless, the PALMprocess can be optimized to replicate minimum radius of curvature ofsuch sharp edges. It should be noted that in some cases, such asenhanced BEFs (as those produced by 3M), some finite (not zero) radiusof curvature is advantageous, as that shown in FIG. 4. These structurescan also be replicable in three-dimensional arrays, resembling lensarrays.

FIGS. 5 and 6 provide SEM (Scanning Electron Microscope)microphotographs of typical non-Lambertian diffusers, produced by thePALM. In FIG. 5, the circular diffusers are shown for various values ofHMFW (Half-Maximum Full Width) angle. In FIG. 6, the ellipticaldiffusers are shown, with different values of the HMFW angle alongperpendicular horizontal axes. Various versions of such diffusers areproducible by the PALM process. Preferably, the major axis of ellipticalmicrostructures is oriented on the image drum in a circumferentialdirection.

BRIEF DESCRIPTION OF THE DRAWINGS

The aforementioned objects and advantages of the present invention, aswell as additional objects and advantages thereof, will be more fullyunderstood herein after as a result of a detailed description of apreferred embodiment when taken in conjunction with the followingdrawings in which:

FIG. 1 is a simplified representation of an architecture of the PALMsystem;

FIG. 2 is an illustration of a two-dimensional projection of a randompattern;

FIG. 3 is an illustration of a two-dimensional projection of adeterministic (repeatable) pattern;

FIG. 4 is a two-dimensional projection of an advanced BEF microstructurewith rounded edges (finite radii of curvature), replicable by PALM;

FIGS. 5A through 5H are views of SEM microphotographs (scale: 20 μm) ofcircular diffusers, with FWHM angles of: (A) 5°; (B) 10°; (C) 20°; (D)40°; (E) 50°; (F) 60°; (G) 70°; (H) 80°;

FIGS. 6A and 6B are views of SEM microphotographs of ellipticaldiffusers;

FIG. 7 is a two-dimensional projection (out of scale) of PALM devicegeometry, including two areas: coating and patterning, as well asprocess regions, denoted as I through IX;

FIG. 8 is an illustration of different liquid wrap angles β₀;

FIG. 9 is an illustration of the kinetics of the PALM process;

FIG. 10 is an illustration (out of scale) of the PALM process,emphasizing fluid coupling;

FIG. 11 is an illustration (out of scale) of a local Cartesiancoordinate system (x, y, z) for the PALM process description, includingheat transfer and thickness of substrate, w, and self-meteringthickness, c;

FIG. 12 is a graph of viscosity coefficient (in logarithmic scale) as afunction of temperature, T, of the adhesive;

FIG. 13 shows the dependence of μ-viscosity coefficient vs. angle β, asa result of β(T) gradient where μ is in logarithmic scale;

FIG. 14 is an illustration of a mechanical clutch, applied to Roll A;

FIG. 15 is an illustration of the adhesive reservoir used in the PALMprocess and showing the transition of the coating from a liquid (lightshade) to a solid (darker shade);

FIG. 16 is an illustration of the substrate and adhesive layers at thecontact between roll B (with nip force P₀) and roll A;

FIG. 17 is a longitudinal temperature gradient into z-direction, in thePALM-modified monolithic process;

FIG. 18 is a representation of a first embodiment of the monolithic PALMprocess;

FIG. 19 is a representation of a second embodiment of the monolithicPALM process;

FIG. 20 is a three-dimensional illustration of the PALM hybrid system,including an innovative patterning part, and standard coating parts;

FIG. 21 is two-dimensional illustration of the PALM system;

FIG. 22 is an advanced version of a PALM system; and

FIGS. 23 through 27 are used to explain a procedure for optimizing wrapangle for different relief pattern sizes.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS General Operation of thePALM System Hybrid PALM Process

The critical elements of the PALM device are shown in simplified form inFIG. 7. For the sake of simplicity we only show elements essential forfunctionality of the device. Two basic areas are shown: the coating areaand the patterning area, the latter one being the subject of theinvention. In the coating area, identified as Region I, the adhesiveliquid (fluid) layer is coated on the continuous substrate band (or,film) with 3-4 mils thickness. This layer is about 30 μm thick andcontains fluid adhesive at room temperature. It is then transferredthrough Region II into idler roll C, and then through Region III, untilit approaches the self-metering puddle (Region IV), where it isintroduced into contact with patterning or image drum A. Here, it is ina vortical mixing area (called the puddle or reservoir) where fluidadhesive is self-metered into Region V, and where adhesive fluidcoupling occurs between the substrate film and patterning drum A. InRegion V, the adhesive is still in liquid form. In this region, thesubstrate band is in contact (coupling) with drum A. In Region VI, theimpression or nip roll B provides a nip force into drum A, in “kiss” (orpressure) contact form. Both nip force and wrap angle β₀ are sufficientto create fluid coupling between the substrate band and drum A, whichhas minimum internal friction force due to fluid coupling. Thepatterning drum A does not have its own driving force; it is driven onlyby solid (or semi-solid) fluid adhesive coupling with substantially thesame angular velocity ω as roll B and the substrate band, in the rangeof 10 revolutions per min.

Roll B also serves the additional function of blocking UV radiation fromRegion V. Therefore, at the same moment that a nip force acts on drum A,the UV radiation starts to cure the adhesive. The wrap angle value, β₀,is in the range of 5°-70° (FIG. 8). In Region VII, UV radiation operateswith intensity of about 5-10 watts/cm². Since FIG. 7 is atwo-dimensional projection of real PALM device geometry, the Region VIIof UV exposure is an extended linear area, with size: Δα·R·l, whereR—radius of drum A, and l—its length (width). The Δα·R-value is 4 cm,for R=8 cm. In Region VII, the transformation (phase change) of liquidinto solid adhesive occurs. After nip force contact, the substrate bandis still in contact with drum A, through angle Δβ, of about 90°. Then inRegion VIII, the substrate band, including solid adhesive layer withreplicated pattern, is transferred to roll D, and then, in Region IX,into double-roll E/E′ that provides the motoric force into thepatterning system. This force drives drum A through coupling Region VII.

Kinematics of the PALM Process

The kinematics of the PALM process is described in FIG. 9. The speed ofthe web band, V, is 20 ft./min., or 10 cm/s, as a reference, since itshould be in this range, for self-metering stability. For roll A radius,R, equal to 10 cm, the angular speed ω, of the roll A, is 1 rad/sec or10 rpm (10 revolutions per minute). In order to calculate the time, t,when the adhesive is within the liquid wrap, with length, s, we assume adiameter of the roll A, D=2r=6 in., and a liquid wrap angle, β₀=30°,then, (s≈Rβ₀),

$\begin{matrix}{{s = {{\pi \; D} = {\frac{\beta_{0}}{360} = {{1.57\mspace{11mu} {{in}.}} = {4\mspace{11mu} {cm}}}}}}{\text{and},}} & (5) \\{V = {{20\mspace{11mu} {{ft}.\text{/}}{\min.}} = {{4\mspace{11mu} {{in}.\text{/}}s} = {10\mspace{11mu} {cm}\text{/}s}}}} & (6)\end{matrix}$

thus, the liquid wrap time, t, is

$\begin{matrix}{t = {\frac{s}{V} = {\frac{4\mspace{11mu} {cm}}{10\mspace{11mu} {cm}\text{/}s} = {0.4\mspace{11mu} s}}}} & (7)\end{matrix}$

In another example, assuming: D=7 in., β₀=45°, we obtain t=0.7 s.

The typical effective width of the diffuser roll is 36 in., or 91 cm,approximately 1 m width for simplicity. The typical diffuser rolleffective length is 2000 ft., or 600 m. Assuming the speed of the band:V=20 ft./min., the typical total time of the PALM process, T, is

$\begin{matrix}{T = {\frac{2000\mspace{11mu} {{ft}.}}{20\mspace{11mu} {{{ft}.}/{\min.}}} = {100\mspace{11mu} {\min.}}}} & (8)\end{matrix}$

Assuming an effective roll width of 1 m, and a length of 600 m, andassuming a 16:9 digital format of a diffuser screen, we obtain thescreen length of 178 cm, and the number of screens per roll is 337. Thisyields 2700 screens per day, assuming the two-shift (16 hr.) dayoperation; or 675,000 per year for a single machine, assuming 250 daysper year of effective web operation.

General Characteristics of the PALM Process

In FIG. 10, the PALM process is described, including fluid and solidcoupling, and the process is characterized in two coordinate systems: acylindrical system: R, β, x, as in FIG. 10, and a local Cartesian system(x, y, z) as in FIG. 11. The cylindrical coordinate system is introduceddue to cylindrical symmetry of the drum A, where R is the drum radius,and angular coordinate, β, has origin (β=0) in the wrap entry, andβ₀—value at nip force, P₀, location, and β₀+Δβ value at the first(fluid/solid) wrap exit, while UV-radiation operates between β=β₀, andβ=β₀+Δα, at the second (solid) wrap region. In FIG. 11, the second localCartesian coordinate system is introduced to show UV radiation exposureas well as heat transfer from the center into the surface of the drum.The substrate thickness, w, is in the range of 100 μm (4 ml), and theself-metered thickness of adhesive, c, (c=c₁+c₂) is in the range of50μ—(which includes base (c₁) and relief (c₂)).

Solid/Fluid Coupling

The solid adhesive coupling is essential to the PALM because it providesa bearing force on drum A, transferred from the motoric force generatedby the two rolls E and E′, with strong impression forces, through solidwrap, located between β₀ and β₀+Δα. This is also supported by fluidwrap, located between β=0 and β=β₀. Without such couplings, drum A wouldhave to be driven by its own motoric force which could destabilize thekinematics of the system. Because of friction and the rotation of thedrum, the actuating force T is created and which is exponentiallyreduced with β-increasing; thus T_(exit) is smaller than T_(entry) as inFIG. 10. Any element of the film, of angular length dθ, will be inequilibrium under the action of the actuating forces, thus generatingpressure, P, proportional to actuating force T, as shown in FIG. 10. Twocoupling forces are included, pressure P, distribution and the nip forceP₀. The solid wrap creates much stronger coupling than that of the fluidwrap.

In the PALM system, the nip shear force is much stronger than the liquidwrap force. However, for the prior art shallow pattern reliefs(equivalent to low-angle diffusers, for example), the liquid wrap is notused. In contrast, for the deep pattern reliefs, as in the PALM, the nipforce is necessary. Nevertheless, it is only a “kiss” force, assumingthe hybrid (i.e., non-monolithic) process.

For the liquid coupling, the sheer stress, equal to nominal pressure, p,multiplied by friction coefficient, f, is also proportional to adhesiveabsolute viscosity, μ, broadly described by Pettrof's law, or itsmodification applied to this case. The absolute viscosity coefficient, μ(hereafter, a “viscosity coefficient”) is typically measured throughkinematic viscosity. For the PALM purposes, the (absolute) viscosity ishigh. For typical adhesives, μ=3-10 dynes-s/cm²; i.e., much higher thanfor typical lubricants, such as castor oil. The preferred (for fluidcoupling) nip force, P₀, is in the range of 30,000 dynes/cm². Due tolarge viscosity of adhesive in liquid (or semi-liquid) case, and modulusof rigidity, R, of adhesive in solid state, both forces, wrap force(both liquid and solid) and nip force, provide sufficient coupling, inorder to drive drum A. It should be noted that, according to the MaxwellTheory, such highly viscous fluids, like adhesives, have “intermediate”properties, characterized by both viscosity coefficient, μ and a modulusof rigidity, R. According to Landau theory, the μ-value is proportionalto R-value, through relaxation time, ℑ. (Maxwellian relaxation time).(Landau and Lifshitz, Theory of Elasticity, 3^(rd) ed,Butterworth-Heinemann (1986)).

Another important requirement for effective fluid coupling is topreserve its stability to avoid boundary lubrication; i.e., directsolid-to-solid contact. This is achieved by maintaining a sufficientlyhigh value of the characteristic parameter: μω/p, where μ—viscosity,ω—angular velocity, and p—normal pressure, as in FIG. 10 (this parameteris dimensionless). For small values of this parameter, theelastohydrodynamic coupling can collapse to boundary coupling (i.e.direct solid-to-solid contact) that could destroy the microstructurepattern. This parameter value must be maintained in all regions fromβ=0, to β=β₀. This is controlled by regulating the entry web tension,T_(entry), and the outgoing web tension T_(exit), when the fluid isstill in a liquid form, according to the following equation:

$\begin{matrix}{{\ln \; \frac{T_{entry}}{T_{exit}}} = {f\; \beta_{0}}} & (9)\end{matrix}$

where f is friction coefficient. Typical T_(entry)/T_(exit) ratio shouldbe about 2. The f-coefficient, obtained from Equation (9), should be inthe range, when f-function is a linear function of μω/p—parameter,according to modified Pettrof's law. This condition is difficult tomaintain, because the adhesive viscosity is decreasing as a function ofβ, due to heat transfer from the center of the drum, as shown in FIG.11. This heat transfer creates a temperature gradient, with adhesivetemperature increasing by β-increasing, as shown in FIG. 12. Such heattransfer (creating temperature growth by 20° with respect to roomtemperature, by average) is needed to increase penetration of the masterrelief, in order to obtain a good fidelity of submicron details,important for diffusers with large diffraction angles (FWHM≧60°). Forthe same reasons, we can not significantly increase the angular velocityω. Therefore, we need to reduce normal pressure, p, in order to keep theparameter, μω/p, sufficiently high; thus, maintaining elastohydrodynamiccoupling regime (to avoid boundary coupling). But, in that case, wereduce the coupling force. Therefore, in order to keep the totalcoupling force sufficiently high, we need to increase the nip force, P₀,and/or preserve high solid wrap coupling force from the regions betweenβ=β₀ and β=β₀+Δβ, as shown in FIG. 10, by increasing Δβ-value, up to90°, or even higher. This is a complex trade-off process which requiresregulation of the heat gradient (leading to gradient dμ/dβ), as well assuch parameters as ω, p, and P₀. The UV-radiation distribution (definedby intensity, I, and Δα-region, as in FIG. 10) also influences thistrade-off. Such an optimization procedure is needed, especially forhigh-resolution (d˜1 μm), and high-aspect ratio (for (AR)>1)microstructures. A typical μ(β)-dependence is illustrated in FIG. 13.

High Relief Patterning

For high-relief patterning, i.e., three-dimensional replication ofhigh-relief microstructures, both random (diffusers) and deterministic(microprisms), with typical reliefs in the range of 5 μm to 30 μm, up to100 μm, we need to optimize a broad variety of mechanical, fluid, heat,and radiation (UV) parameters, such as: viscosity (μ), surface energy,UV-exposure distribution, actuation force T, nip force P₀, temperaturegradient (dT/dβ), friction coefficient f, modulus of rigidity (R), drumangular (and linear) velocity (ω), wrap angles (β₀, Δβ), as well asself-metering thickness (c), partial thicknesses: c₁ and c₂ and levelingtime.

A number of critical factors determine high-quality high-reliefpatterning of microstructure, both deterministic (such as microprisms)and random (such as diffusers), including:

1. Liquid coupling (a wrap, with angular size β₀)

2. Solid coupling (a wrap, with angular size, Δβ)

3. Nip force from contact between roll B and roll A

4. Reservoir of adhesive (at the input of liquid wrap)

5. Heat transfer (at the liquid (fluid) wrap)

6. Distributed UV radiation (with angular size, Δα).

The factors (1), (3), (4), and (5) define self-metering of the PALM. Thefactors (2) and (6) define solid/liquid coupling-based driving of theroll A.

Another critical factor is a combination of the UV radiationdistribution, with monotonic decreasing of the coupling pressure, p, asa function of angle β. The latter feature is a consequence of simplemechanical law, coming from the mechanical clutch effect, as shown inFIG. 14. The actuation force, T, creates reaction force dP, at thedecrement dθ; thus,

dT=fdP   (10)

where f—friction coefficient; also we have

dP=Tdθ  (11)

substituting Equation (11) into Equation (10), we obtain

dT=fTdθ  (12)

and, after integration, we have

T(θ)=T _(entry) e ^(fθ)  (13)

which is equivalent to Equation (9). The reaction force P, createspressure, p, on the drum, as a normal force P per unit surface, in theform (l is the length of the drum A)

dP=plrd6   (14)

where lrdθ, is surface element. Using Equations (11), (13), and (14), weobtain the following relation for pressure, p, as a function of angle θ,

$\begin{matrix}{p = {\frac{T}{lr} = \frac{T_{entry}^{{- f}\; \theta}}{lr}}} & (15)\end{matrix}$

which shows that pressure, p, is reduced exponentially as a function θ,into direction of motion. This effect, together with UV radiationdistribution creates the stable conditions of disengagement of adhesivefrom the master roll A.

The UV radiation is distributed along angle β, between β=β₀ (nip forcelocation), and β=β₀+Δα. In the three-dimensional case, ideally, it isdistributed cylindrically, into the drum A axis. Assuming that UVradiation source linear intensity is 300 W/in., or 118 W/cm, andassuming that Δα=90° (or, π/2), and R=10 cm, so rΔα=15.7 cm, and thesource intensity, I, is

I=118 W/15.7 cm²=7.5 W/cm²   (16)

PALM integrates coating, self-metering, and replication processes. Forthese purposes, we need to discuss the meaning of surface energy, γ, forboth adhesive, substrate, and roll A master, in order to obtain asufficiently high wettability of the substrate and master, and theadhesion of coating (adhesive). The well-known condition for goodwettability and adhesion, is

γ_(s)≧γ_(a)   (17)

where indices “s” and “a” mean substrate and adhesive, respectively.Surface activation is used to increase the wettability of the substrateand the adhesive of the coating. The most common are the followingtreatments: flame, plasma, and corona, the latter one mainly used forweb application. Applied to the substrate, it increases its surfaceenergy, which, in general, has two components: dispersive, and polar(typical surface energies, in dynes/cm, are: 18-20 (for Teflon); 41-49(for PET); 46 (for polycarbonate); and 47 (for glass):

γ=γ^(d)+γ^(p)   (18)

The dispersive component represents the non-polar Van-der-Waals (London)forces, and the polar component represents the polar Van-der-Waalsforces, connected with permanent electrostatic dipole interactions andhydrogen bond forces. The corona treatment, for example, improves theseinteractions; thus increasing substrate surface energy, and inconsequence, improving adhesion Equation (17). Equation (17) should beused for the PALM coating, wettability and adhesion of adhesive inrespect to the substrate and in respect to the master during liquidcoupling, and during solid coupling.

Basic Steps of the PALM Process

The following are the steps of the PALM process:

-   -   Coating (and surface activation) (Step 1)    -   Wetting of the Master (by Reservoir) (Step 2)    -   Liquid Coupling (and Temperature Treatment) (Step 3)    -   Nip Force Action and Self-Metering (Step 4)    -   UV-Radiation Exposure and Adhesion of Adhesive Pattern into        substrate (Step 5)    -   Disengagement (or, release) of the Adhesive Patterns from the        Master, and Surface Energy Interaction (Step 6).

These six (6) basic steps of PALM reinforce and cross-interact with eachother. Some of them were previously discussed.

STEP 1: This step is only ancillary to the PALM process, but it shouldalso be carefully carried out for high-quality PALM purposes. The webband (a film) consists of a flexible plastic substrate such aspolycarbonate, about 100 μm thick. It should be highly uniform to avoidmicro-bends. It should be pre-treated for better adhesion andwettability. The adhesive should be coated as uniformly as possible.Some adhesives' non-uniformities are cancelled by the nip force, and thereservoir also stabilizes the adhesive flow.

STEP 2: After STEP 1, the film (band) consists of the substrate coatedwith adhesive in liquid form. In the PALM process, the film comes incontact with the image drum (roll A) prior to impression roll B, in theform of adhesive excess, called a self-metering puddle, or reservoir.Creation of a reservoir for adhesive is a feature of PALM, allowingpre-wetting of the master roll A. This reservoir of adhesive should bein a vortical (not laminar) stage, in order to maximize the pre-wettingprocess. The reservoir, shown in FIG. 15, also stabilizes the liquidadhesive flow. In a case where the speed of the drum A is substantiallylower than 10 rpm, the volume of reservoir will be excessively large,while in a case of too-high speed of drum A, substantially higher than10 rpm, the volume of the reservoir can almost vanish, creatingun-wanted boundary coupling between rolls A and B. In general, thepresence of the reservoir allows for small non-uniformities of adhesiveflow; thus, regulating its constant volume rate through contact betweenthe web band (film) and master roll A.

STEP 3: The liquid coupling is essential for the PALM, especially forhigh-relief replications. It allows substantially filling evenhigh-relief master pattern valleys with an adhesive layer of thickness,c, (about 30 μm) which consists of its base sub-layer, c₁, and adhesiverelief sub-layer, c₂, as shown in FIG. 16, for the roll B/A-contact. Theliquid coupling also supports the bearing of roll A. The presence of theliquid wrap is essential for high-quality replication of high-reliefmicropatterns. Its presence allows also for heat transfer from theinterior of the roll A, in order to reduce adhesive viscosity for betterfilling of master surface relief. The presence of the substantial basesub-layer (so-called residual thickness), with thickness, c₁, is alsoessential in order to obtain a strong “stalactite” type structure (byanalogy to caves' stalactites). The high strength of “stalactite”(especially at “valleys,” as in FIG. 16) is important for the purpose ofthe overall strength of adhesive relief structure, especially during thestructure's disengagement in STEP 6.

STEP 4: All three steps (2), (3), and (4), allow for the self-meteringof the PALM. The self-metering simplifies the PALM process to a largeextent, as expensive pre-metering equipment such as slot coatingapplicators are not needed to apply the coating (adhesive) fluid. Thus,simpler coating applications can be used to apply the radiation curablecoating fluid on the substrate. When a nip roll is used in the meteringzone, the radial pressure and the tensions change self-consistently,making the metering substantially independent of the incoming fluidvolume, due to STEP 6, as well as due to STEPS 2 and 3.

In summary, at the wrap of the drum A and the web, the coating isself-metered by the tension of the web band around the drum, as well bythe nip force. The nip pressure should be in the range of 1-30 lb./in.².In addition, the nip force also stabilizes thickness, c₁, of the baselayer making it uniform, in spite of some non-uniformities of thecoating process. For the purposes of the summary of the PALM process,there are several important events at the interface of the drum (roll A)and the web (film-band, and roll B). They are:

-   -   Conforming of the liquid coating (adhesive) into the master        pattern (STEPS 2, 3 and 4)    -   Change of viscosity of the coating from a high value to a lower        value due to thermal gradients (STEP 3)    -   Thermal equilibrium of the coating (STEP 3)    -   Radiation curing followed by phase change of the coating from a        liquid to a solid (STEP 5)    -   Release of the cured coating from the master pattern (STEP 6).

This process must proceed continuously for the entire length of the webstock.

STEP 5: The UV-radiation, in the range of 10 W/cm², should be uniformlydistributed at the cylindrical area with angular dimensions, Δα, in therange of 90°, or π/2, and linear dimensions: rΔα, and l, where r isabout 10 cm, and l is about 1 m. This area is equal to, or slightlyexceeds the solid coupling (wrap) area, with angular dimensions Δβ. Thetime of exposure, t_(E), can be computed from Equation (7), where lengths, is replaced by RΔα; i.e., for R=10 cm, Δα=π/2, and V=10 cm/s, weobtain

$\begin{matrix}{t_{E} = {\frac{R\; \Delta \; \alpha}{V} = {{\left( \frac{\pi}{2} \right)\frac{10\mspace{11mu} {cm}}{10\mspace{11mu} {{cm}/s}}} = {1.6s}}}} & (19)\end{matrix}$

and, for I=7.5 W/cm², the exposure of UV-radiation is 12 J/cm². Duringthe UV-exposure process, the adhesive layer is cured (hardened) intosolid form. In FIG. 11, the geometry of this process is presented, withlocal Cartesian coordinate system, directed (z-axis) into the center ofthe roll A. The origin of this coordinate system (z=0) is at theinterface between substrate and adhesive surfaces. During the exposureprocess two critical effects occur: (1) increasing of surface energy,γ_(a), of the adhesive layer (and, of the substrate layer); (2)increasing of transmissivity of adhesive layer due to phase change. Thisprocess starts at z=0 and progresses in the z-direction. Therefore, theadhesivity of the substrate-adhesive interface must be a priori high.The direction of UV-radiation can be also in the opposite (to z-axis)direction. However, the positive direction (into z>0) of UV radiation ispreferable, since, in such a case, the adhesive base layer, (c₁) iscured first, to create the stable base for the adhesive micro-pattern.

STEP 6: At the end of the PALM process, the self-metered phase changingcoating needs to attach to the substrate and not to the master pattern.This is accomplished by interaction (matching) surface energies of thevarious interfaces. Two effects stabilize this disengagement process ofrelieving solid adhesive from the master pattern: (1) increasing surfaceenergy of adhesive due to UV-exposure, and (2) reducing of normalpressure of the web, p, with β-angle increasing, as in Equation 15).Also, cooling of the solid wrap, by cold nitrogen flow, for examplewould be preferred, especially for high surface reliefs.

Monolithic PALM Process

In an embodiment of the PALM process for replication of a monolithicpattern, the adhesive layer is replaced by a partially melted dielectricsubstrate layer, due to applying temperature distribution, as in FIG.11, to almost the melting point of the substrate. Due to a temperaturegradient in the z-direction, as in FIG. 17, the higher-z sub-layers ofthe substrate will have higher temperature than lower-z sub-layers.Thus, the higher-z sub-layers will be more melted then lower-z ones. Inaddition, we need to apply extra pressure, both from tension (actuation)forces, T, and from impression force, P₀. The latter force will nolonger be a nip (or “kiss”) force, but instead will be a strong pressureforce. In addition, it is necessary to apply intensive cooling of thesolid wrap, preferably by cold nitrogen gas flow. In such a case, thesubstrate monolithic pattern can be effectively removed from the masterpattern; thus creating a substrate monolithic surface relief pattern.

In the alternative version of the monolithic PALM process we still applyadhesive, as in Region III of FIG. 7, but the role of the substrate isonly auxiliary, being only transporter for the adhesive layer. Then,Regions IV, V, VI, an VII are repeated as in FIG. 7, except substratesurface energy must be sufficiently high to transport the adhesive withrelief pattern as in FIG. 16, but not too high to enable laterdisengagement from the adhesive layer; see Equations (17) and (18).These equations have to be carefully applied to optimize thisdisengagement process, as well as applying cold nitrogen flow to improvecuring process in Region VII. Then, just after disengagement, in RegionVIII, the adhesive, still in semi-solid form, should be coated on anauxiliary low-cost protective substrate, applied for mechanicalstability purposes. This stability is needed to provide securetransportation of the resulting product. As a result, we obtain themonolithic diffuser film, with removable protection layer. This is incontrast to the hybrid diffuser film; i.e., diffuser coated on asubstrate, as in FIG. 11.

For purposes of this invention, we propose two versions of themonolithic PALM process; A and B. Version A, discussed above, has beenillustrated in FIG. 18. We see that the Regions I through VIII, are thesame as in FIG. 7, but the Regions IX, X, XI, XII, and XIII are new ones(Region IX is different from that in FIG. 7). Also, rolls F, G, H, K arenew ones.

In order to disengage the substrate (S) from the adhesive (A) film withthree-dimensional-micropattern, obtained from the patterning roll A,heat treatment is provided in Region XI; thus, substrate (S) is rolledinto roll H in Region XIII. In parallel, differential adhesive (PSA) istransported from roll G in Region X into roll F. Since this adhesive isvery sticky, it will attract epoxy (adhesive A), to serve as itsstrength-protective substrate, to transport it into Region XII and rollK. As a result, the micropatterning film, obtained in this A-version ofthe monolithic PALM process (MPP), will be rolled out on the roll K,without substrate (S).

In version B of the monolithic PALM process, the process is furtherremoved from the hybrid version. Instead of Regions I and II, the epoxytank is introduced for coating purposes, as shown in FIG. 19. Due to useof a looped belt in Region XIV, the epoxy reservoir is created, creatinga self-metering process as in FIG. 7. Then, it is guided into a spacebetween patterning roll A, and the belt between rolls C, B and L. Aftercuring in Region XV, by UV radiation, it is removed from the roll A dueto vacuum drum M, and heat treatment, as shown in FIG. 19. As a result,the micropatterning film, obtained in this B-version of the PALM processwill be rolled out, without substrate; or, in alternative version, willbe coated on the differential adhesive (PSM), as a strength-protectivesubstrate for easier transportation (into customer).

There are two particularly unique aspects of VERSION B: (1) Epoxy isused which is not self-consistent material, i.e., it is created fromliquid form. In contrast, prior art systems apply only self-consistentmaterials such as resins. (2) An extra belt (rolls C, B and L) isapplied to form the epoxy film and to provide the self-metering vorticalreservoir feature of the invention.

Advanced Design of the PALM for Large-Scale Webs

In the case of large-scale PALM webs, with roll widths of 2 m, or evenhigher, the hybrid structure of the PALM device cannot be used. By“hybrid” structure, we mean that the patterning (casting) PALM device,constitutes only the “patterning station” part of the overall device asin FIG. 20 (three-dimensional version), or FIG. 21 (two-dimensionalversion), while remaining parts are adapted from standard imprintingweb. In contrast, in the case of a new generation of a large-scale PALMweb, all web stations, not only patterning ones, need to be designed anddeveloped.

In order to mitigate the non-uniformities of the tension forces, theinvention uses elastomer rollers rather than rigid rollers. Since filmgenerally is thin (about 4 mills), the inertia will createextra-tension, especially in the case of large-scale webs. Therefore, toavoid over-stretching (plastic deformation), a synchronized drive isrecommended, rather than single motoric force drive, as in FIG. 7. Thiswill add to the complexity of the system but, it will mitigate tensionforce non-uniformities that would damage the film. Also, distancesbetween rollers should be as small as possible to avoid plasticdeformation. For the same reason, lighter carbon composite rollers (samestrength, but lighter) should be used to minimize the amount of inertia,in order to minimize driving force to rotate the rolls. All of theseimprovements, applicable for large-scale webs, are deemed to be aprotected embodiment hereof.

Synchronizing the drive to avoid over-stretching and plastic deformationmay be accomplished by controlling the motor speed at each driven rolleror drum. In the present invention such speed control is preferablyimplemented by providing sensors at each driven roller to locally sensefilm tension. The signals generated by such sensors are input to acentral processing unit which then sends out motor speed control signalsto each driven roller. Thus, the sensors, central processing unit anddrive motors from a feedback-based sensor network that effectivelysynchronizes roller speeds to preclude any excessive local tension thatcould otherwise damage the film by permanent deformation or evenbreakage.

One significant feature of an advanced PALM system is shown in FIG. 22as an adjustable position idler roll C which would provide an optimumliquid wrap angle β₀. This parameter would be selected to provide thebest replication results for the particular microstructure patterninvolved, which brings us to the following discussion:

Optimization Procedure for Wrap Angles as a Function of Relief PatternSize

The existence of self-metering and adhesive reservoir is especiallycritical for random structures such as diffusers, since it allows forself-stabilization of liquid adhesive flow, independently on δ-localvalue (see FIG. 2). It is also useful for deterministic (periodic)structures as in FIGS. 3 and 4. When δ-r.m.s is growing, thus,β₀-optimum value is also growing, as shown in Table 1, where the optimumβ₀-values have been given, for specific patterning roll (A) radius, R≅10cm.

TABLE 1 δ <1 μm 1–2 μm 2–5 μm 5–10 μm 10–20 μm 20–50 μm 50–100 μm(β₀)min. 0°  5° 10° 20° 30° 30° 30° (β₀)max 70°  70° 70° 70° 70° 70° 70°(β₀)opt 0° ~5° ~30°   ~45°   ~55°   ~60°   ~65°  We see that the high-quality web operation is possible only within therange

(β₀)_(min)≦(β₀)≦(β₀)_(max)   (20)

where (β₀)_(max) and (β₀)_(min) are upper and lower bounds. The optimum(β₀)-value is within the range determined by Equation (20). We see thatwhile lower the bound increases δ-value, the upper bound can not exceed70°. Then, reservoir volume, Ω_(r), is too small to preserveself-motoring.

In Table 1, the experimental values are presented, obtained fromchanging of (β₀)-value (see FIG. 7). This is also illustrated in FIG. 8.For example, for δ=2-5 μm (critical r.m.s. value for large-anglediffusers (see FIG. 5)), where δ≅5 μm, for FIG. 5( g), we have(β₀)_(opt)˜30°, for R=10 cm (the radius of patterning A-roll, as in FIG.5). There are a lot of combination of R-values, and β₀-values; thus, theexperimental procedure (trying many prototypes with various (R,β₀)-combinations) can be very expensive and time-consuming.

Therefore, the theoretical optimization procedure should be given, inorder to identify the Region of Interest (ROI) of t_(w), and Ω_(r)values, where Ω_(r) is reservoir volume (Ω_(r)=l·A_(r); A_(r)—reservoirarea), and t_(w) is wrap time, in the form:

$\begin{matrix}{t_{w} = \frac{\left( \beta_{0} \right) \cdot R}{V}} & (21)\end{matrix}$

where V is linear roll speed, as V=10 cm/s in Equation (6). Theoptimization procedure should start from developing proper roll speedvalue. This is because the geometry of the UV-source is determined;defined by Δα·R in FIG. 7, as well as adhesive's required UV-exposure,E, and the intensity of UV-source; I, thus, the required exposure timecan be found from the relation:

$\begin{matrix}{t_{E} = {\frac{E}{I}.}} & (22)\end{matrix}$

For example, for our adhesive, the required UV-radiation exposure is 12J/cm² (this is quite a high value, but the adhesive layer is quitethick), and UV-source intensity is 7.5 W/cm²; thus, t_(E)=1.6 s (seeEquation (16)). However, s=Δα·R is also known, because source spreadarea is known (e.g., s≅16 cm); thus, from

$\begin{matrix}{t_{E} = \frac{s}{V}} & (23)\end{matrix}$

we can find roll speed: V=s/t_(E)=16 cm/1.6 s=10 cm/s, as in Equation(16). Therefore, the roll speed is determined by adhesive material'ssensitivity (E), UV-source intensity (I), and source spread linear area(s). Having V-value, we can use Equation (21). In general, the wraptime, t_(w), has to grow with δ-value increasing, because for largersizes of relief pattern, more time is required to fill patterninggrooves (see FIG. 15), leading to increasing β₀-value, as in Table 1.For specific speed (V) and specific R-value, wrap time t_(w) isproportional to β₀-value, as in Equation (22). However, also reservoirvolume Ω_(r), should increase. It is illustrated in FIG. 23, as:

Ω_(r)Ω_(T)−Ω₀−Ω′  (24)

where Ω_(T) is the volume of the space including total cross-section(triangle ABC), and roll length l, in the form

$\begin{matrix}{{{\Omega_{T} = \frac{R^{2}l}{2\mspace{11mu} \tan \; \beta_{0}}};}{A_{T} = \frac{R^{2}}{2\mspace{11mu} \tan \; \beta_{0}}}} & (25)\end{matrix}$

where A_(T)-cross-section area (Ω_(T)=lA_(T)); thus, instead of Equation(24), we can write

$\begin{matrix}{{A_{r} = {A_{T} - A_{0} - A^{\prime}}}\text{where}} & (26) \\{{{A_{0} = {\left( {\frac{\pi}{2} - \beta_{0}} \right)\frac{R^{2}}{2}}},{A^{\prime} = {\frac{1}{2}{R^{2}\left( {\frac{1}{\sin \; \beta_{0}} - 1} \right)}^{2}\tan \; \beta_{0}}}}{\text{thus},}} & (27) \\{A_{r} = {\frac{R^{2}}{2}\left\lbrack {\frac{1}{\tan \; \beta_{0}} - \frac{\pi}{2} + \beta_{0} - {\left( {\frac{1}{\sin \; \beta_{0}} - 1} \right)^{2}\tan \; \beta_{0}}} \right\rbrack}} & (28)\end{matrix}$

or, the normalized reservoir area, is

$\begin{matrix}{{Ar}_{n} = {\frac{2A_{r}}{R^{2}} = {{f\left( \beta_{o} \right)} = {\frac{1}{\tan \; \beta_{0}} - \frac{\pi}{2} + \beta_{0} - {\left( {\frac{1}{\sin \; \beta_{0}} - 1} \right)^{2}\tan \; \beta_{0}}}}}} & (29)\end{matrix}$

In order to check the correctness of Equation (29), we obtain

$\begin{matrix}{{\frac{A_{r}}{\beta_{o}} = {0 = {R^{2}\left( \frac{1 - \pi}{4} \right)}}},{{\text{and}\mspace{14mu} \frac{A_{r}}{\beta_{o}}} = {\frac{\pi}{2} = 0.}}} & (30)\end{matrix}$

The second limit explains why the upper bound of β₀-value can notachieve 90%, as in Table 1. For small β₀-values, we have:

$\begin{matrix}{A_{m} \cong {2 - \frac{\pi}{2} - {\frac{3}{2}\beta_{0}}}} & (31)\end{matrix}$

so, indeed, in the limit of β₀=0, we obtain Equation (30); similarly forβ₀=π/2. The general relations Equations (29) and (31) have been shown inFIGS. 24 and 25.

We see that, from Equations (21) and (29), we have

$\begin{matrix}{t_{w} = {\frac{\beta_{0}R}{V} = {aR}}} & (32)\end{matrix}$

where a is proportionally constant, and

$\begin{matrix}{A_{r} = {{\frac{R^{2}}{2}{f\left( \beta_{0} \right)}} = {b^{2}R^{2}}}} & (33)\end{matrix}$

where, f(β₀) is determined by Equation (29). Eliminating R-value fromthese equations, we obtain

$\begin{matrix}{\frac{t_{w}}{\sqrt{A_{r}}} = {\frac{a}{b} = \frac{\beta_{0}}{\sqrt{\frac{f\left( \beta_{0} \right)}{2}}}}} & (34)\end{matrix}$

which is illustrated in FIGS. 26 and 27.

We see that in order to increase t_(w)(o) value, for fixed R, we needindeed to increase β₀-value, as in Table 1. On the other hand, forlarger β₀-values (required for larger surface reliefs), we need toincrease R-value in order to accommodate larger t_(w)-values, while topreserve also reasonable large √{square root over (A_(r))}-values.

Having thus disclosed preferred embodiments of the present invention, itwill be understood that various modifications and additions arecontemplated. Accordingly, the scope hereof is to be limited only by theclaims appended hereto and their equivalents.

1. A method of replicating three-dimensional Microstructures from animage drum having a master pattern of microstructures onto a continuousrolling substrate band of curable adhesive-coated flexible planarmaterial; the method comprising the steps of: a) positioning a niproller in proximate parallel relation to said image drum; b) rollingsaid adhesive-coated material between said nip roller and said imagedrum with said adhesive in an uncured liquid state, said adhesive-coatedmaterial being wrapped on said image drum through a selected angle offrom 5° to 70° prior to reaching said nip roller; c) wrapping saidadhesive-coated material around said image drum through a selected angleexceeding 90° beyond said nip roller; d) applying ultraviolet radiationto said adhesive-coated material beyond said nip roller to cure saidadhesive; and e) feeding said cured adhesive-coated material between apair of motorized compression rollers to continuously pull said materialaround said image drum.
 2. The method recited in claim 1 furthercomprising the step of applying a sufficient amount of liquid adhesiveto said material to form a self-metering reservoir of said liquidadhesive between said material and said image drum prior to said niproller.
 3. The method recited in claim 2 wherein said applying stepcomprises the step of allowing a vortex mixing action to occur in saidreservoir of liquid adhesive.
 4. The method recited in claim 1 furthercomprising the step of utilizing heat transferred from the interior ofsaid image drum to the exterior of said drum to decrease the viscosityof the liquid adhesive coating to increase the penetration of thecoating into the master pattern of microstructures.
 5. The methodrecited in claim 1 wherein step a) comprises the step of positioningsaid nip roller to apply a selected pressure against saidadhesive-coated material between said nip roller and said image drum. 6.The method recited in claim 5 further comprising the step of controllingthe nip roller pressure and the liquid selected wrap angle in step b) toform a base sub-layer of adhesive which is of substantially uniformthickness and a relief sub-layer of adhesive whish substantiallyconforms to the microstructure profile on said image drum.
 7. The methodrecited in claim 1 further comprising the step of placing said niproller in a position to optically block said ultraviolet radiation fromsaid adhesive-coated material prior to said material reaching said niproller.
 8. An apparatus for replicating three-dimensionalmicrostructures from a master pattern of microstructures onto acontinuous rolling substrate band of curable adhesive-coated flexibleplanar material; the apparatus comprising: an image drum having saidmaster pattern of microstructures on a peripheral surface; a nip rollerpositioned in proximate parallel relation to said image drum; saidadhesive-coated material being wrapped partially about said image drumand between said nip roller and said image drum with said adhesive in anuncured liquid state before said nip roller and in a curing and curedstate beyond said nip roller; a source of ultraviolet radiationpositioned for curing said adhesive-coated material beyond said niproller; and said uncured wrap of said material about said image drumbeing along a selected angle of between 5° and 70°, said curing andcured wrap of said material about said image drum being along a selectedangle of more than 90°.
 9. The apparatus recited in claim 8 furthercomprising a sufficient amount of liquid adhesive applied to saidmaterial to form a self-metering reservoir of liquid adhesive betweensaid material and said image drum prior to said nip roller.
 10. Theapparatus recited in claim 8 further comprising a source of heat in saidimage drum for reducing the viscosity of said uncured adhesive on saidflexible planar material and increasing the penetration of said adhesiveinto said master pattern of microstructures.
 11. The apparatus recitedin claim 8 wherein the nip roller is positioned to apply a nip forceagainst said substrate within a range of from 1 to 30 lb/cm² percentimeter of width.
 12. The apparatus recited in claim 8 wherein saidsource of ultraviolet radiation applies a uniform distribution of UVradiation with an intensity of between 5 to 10 Watts/cm².
 13. Theapparatus recited in claim 8 wherein said nip roller is furtherpositioned relative to said image drum to optically block saidultraviolet radiation from said rolling substrate band before said niproller.
 14. A method of replicating three-dimensional microstructuresfrom an image drum having a master pattern of microstructures onto acontinuous rolling substrate band of curable adhesive-coated flexibleplanar material; the method comprising the steps of: a) positioning anip roller in proximate parallel relation to said image drum; b) rollingsaid adhesive-coated material between said nip roller and said imagedrum with said adhesive in an uncured liquid state, said adhesive-coatedmaterial being wrapped on said image drum through a selected angle offrom 5° to 70° prior to reaching said nip roller; c) applying asufficient amount of liquid adhesive to said material to form aself-metering reservoir of said liquid adhesive between said materialand said image drum prior to said nip roller; d) wrapping saidadhesive-coated material around said image drum through a selected angleexceeding 90° beyond said nip roller; and e) applying ultravioletradiation to said adhesive-coated material beyond said nip roller tocure said adhesive.
 15. The method recited in claim 14 furthercomprising the step of placing said nip roller in a position tooptically block said ultraviolet radiation from said adhesive-coatedmaterial prior to said material reaching said nip roller.
 16. The methodrecited in claim 14 wherein said applying step comprises the step ofallowing a vortex mixing action to occur in said reservoir of liquidadhesive.
 17. The method recited in claim 14 further comprising the stepof feeding said cured adhesive-coated material between a pair ofmotorized compression rollers to continuously pull said material aroundsaid image drum.
 18. The method recited in claim 14 further comprisingthe step of utilizing heat transferred from the interior of said imagedrum to the exterior of said drum to decrease the viscosity of theliquid adhesive coating to increase the penetration of the coating intothe master pattern of microstructures.
 19. The method recited in claim14 wherein step a) comprises the step of positioning said nip roller toapply a selected pressure against said adhesive-coated material betweensaid nip roller and said image drum.
 20. The method recited in claim 14further comprising the step of controlling the nip roller pressure andthe liquid selected wrap angle in step b) to form a base sub-layer ofadhesive which is of substantially uniform thickness and a reliefsub-layer of adhesive whish substantially conforms to the microstructureprofile on said image drum.
 21. An apparatus for replicatingthree-dimensional microstructures from a master pattern ofmicrostructures onto a continuous rolling substrate band of curableadhesive-coated flexible planar material; the apparatus comprising: animage drum having said master pattern of microstructures on a peripheralsurface; a nip roller positioned in proximate parallel relation to saidimage drum; said adhesive-coated material being wrapped partially aboutsaid image drum and between said nip roller and said image drum withsaid adhesive in an uncured liquid state before said nip roller and in acuring and cured state beyond said nip roller; a sufficient amount ofliquid adhesive applied to said material to form a self-meteringreservoir of liquid adhesive between said material and said image drumprior to said nip roller; a source of ultraviolet radiation positionedfor curing said adhesive-coated material beyond said nip roller; andsaid uncured wrap of said material about said image drum being along aselected angle of between 5° and 70°, said curing and cured wrap of saidmaterial about said image drum being along a selected angle of more than90°.
 22. The apparatus recited in claim 21 wherein said nip roller isfurther positioned relative to said image drum to optically block saidultraviolet radiation from said rolling substrate band before said niproller.
 23. The apparatus recited in claim 21 further comprising a pairof motorized compression rollers continuously pulling said materialaround said image drum.
 24. The apparatus recited in claim 21 furthercomprising a source of heat in said image drum for reducing theviscosity of said uncured adhesive on said flexible planar material andincreasing the penetration of said adhesive into said master pattern ofmicrostructures.
 25. The apparatus recited in claim 21 wherein the niproller is positioned to apply a nip force against said substrate withina range of from 1 to 30 lb/cm² per centimeter of width.
 26. Theapparatus recited in claim 21 wherein said source of ultravioletradiation applies a uniform distribution of UV radiation with anintensity of between 5 to 10 Watts/cm².
 27. The method recited in claim1 further comprising the step of separating said cured adhesive fromsaid material.
 28. The method recited in claim 27 wherein saidseparating step employs heat to separate said cured adhesive from saidmaterial.
 29. The method recited in claim 27 further comprising the stepof applying a protective film to said cured adhesive after saidseparating step.
 30. The method recited in claim 1 further comprisingthe step of providing a wrap angle roller to support said uncured liquidadhesive coated material at an appropriate position relative to said niproller and said image drum to provide said selected wrap angle of from5° to 70°; and altering the position of said wrap angle roller toprovide an optimum selected wrap angle within said 5° to 70° range ofselected wrap angles.
 31. A method of replicating a master ellipticaldiffuser microstructure pattern located on an image drum onto acontinuous rolling substrate band of curable-adhesive coated flexibleplanar material, the method comprising the steps of: an image drumhaving said master pattern of microstructures on a peripheral surface; anip roller positioned in proximate parallel relation to said image drum;said adhesive-coated material being wrapped partially about said imagedrum and between said nip roller and said image drum with said adhesivein an uncured liquid state before said nip roller and in a curing andcured state beyond said nip roller; a sufficient amount of liquidadhesive applied to said material to form a self-metering reservoir ofliquid adhesive between said material and said image drum prior to saidnip roller; a source of ultraviolet radiation positioned for curing saidadhesive-coated material beyond said nip roller; and said uncured wrapof said material about said image drum being along a selected angle ofbetween 5° and 70°, said curing and cured wrap of said material aboutsaid image drum being along a selected angle of more than 90°.
 32. Themethod recited in claim 31 further comprising the step of orienting themajor axis of said elliptical microstructures on said image drum in acircumferential direction.
 33. A roll-to-roll web-based method ofreplicating a three-dimensional microstructure pattern from an imagedrum onto a cured adhesive; the method comprising the steps of: a)positioning a nip roller in proximate parallel relation to said imagedrum; b) forming a looped belt between said nip roller and said imagedrum, said belt being partially wrapped about said image drum through aselected wrap angle of from 5° to 70° prior to said nip roller; c)applying an uncured liquid adhesive between said belt and said imagedrum in sufficient quantity to form a self-metering reservoir of saidliquid adhesive for flowing onto said image drum and said microstructurepattern; d) curing said adhesive on said image drum; and e) releasingsaid cured adhesive from said image drum, said cured adhesive having areplicated version of said microstructure pattern.